1. Field of the Invention
The present invention relates to flexible prefabricated sealing membranes based on bituminous binder used principally to seal the roofs of buildings, works of art or the like, and has for its object such a membrane based on modified polyurethane bituminous binder, as well as its process for production.
2. Description of the Related Art
There have been known for numerous years membranes that are bituminous based modified by polymers of the SBS (Styrene Butadiene Styrene) type or PPA (Polypropylene Atactique), which have been widely used from the 1970s in the sealing of terrace roofs.
The modification of the bitumens from refineries by direct distillation is a requirement. Thus, the conventional bitumens used particularly in the roadway industry have softening points of the order of 40° C. and from −5° C. are hard and break light glass.
However, these temperatures of use are too limiting for use in roofing in the scope of which the range of temperature as a function of climate varies between −40° C. and 110° C.
It is thus necessary to modify the bitumen. The conventional techniques consist in modification by thermoplastic polymers of the type for example of block elastomers [SBS, SEBS (for Styrene Ethylene Butadiene Styrene), . . . ] or plastomers [Polyolefin of the type of PPA, EVA, PPI, APAO (for amorphous α polyolefin)].
Thus, by SBS modification, there can be obtained a bituminous binder having a softening point of the order of 125° C. and flexibility at a low temperature of the order of −30° C. The range of use of a binder modified by plastomer polymers is generally comprised between −15° C. and 150° C.
However, membranes made from bituminous binder modified by the mentioned polymers have their limits: these polymers are sensitive to UV and, because of this, the last layer (the visible layer) requires a specific supplemental protection against attack by UV.
This protection, when it is integrated into the prefabricated membrane, is at present provided either by metallic flakes (aluminum, copper or stainless steel), or by flakes or granules of slate or mica sprinkled on the surface during the production process. These so-called “autoprotective” protections entail an extra weight that can range up to 1.5 kg/m2, representing up to 30% by weight of the membrane and increasing the price of the final membrane.
In addition to UV, these known mentioned products age rapidly relative to the lifetime of their structures and degrade by oxidation, thereby failing to provide suitable sealing for a long period of time. Resealing thus is necessary on the average every 15-20 years.
For several years there have been developed modified polyurethane bituminous coatings. These products have above all an application in road coverings and the sealing of works of art and buildings. The known products of this type are namely:                applicable cold: the product is present in liquid form, mono or bicomponent, and attains its characteristics once crosslinked.        applicable hot: the polymerization takes place in the hot bitumen just before its application to the worksite.        
For example, French patent No. 2 064 750 discloses a thermoplastic bituminous binder containing up to 10% of polyurethane. The polyols used have functionalities greater than 2, up to 8. The binder keeps its thermoplastic properties because of the low proportion of polymer.
This process described in the French patent mentioned above requires a mixture at the worksite at high temperatures that can reach 200° C.
Moreover, from European patent application No. 1 013 716 of Dec. 23, 1999 in the name of the applicant, there is known a monocomponent liquid composition that is based on bitumen and polyurethane, applicable cold to a support to be sealed.
However, the known products from the French and European applications mentioned above are not adapted for the production of membranes prefabricated in a factory.
From the document WO 97/03253 is known a sheet material forming a barrier against moisture and comprising a layer of a mixture of bitumen/polyurethane spread on a polymeric film and covered with a detachable film.
The polymer film ensures protection of the bituminous layer against external agents, particularly against UV, and said bituminous layer has the properties of cold adhesivity and does not need to be reheated before application of the sheet material.